replacing values in a column with another column R

Question

I have two tables in different dimensions, now I want to replace value datA$swl1 with values in datB$swl2 according to userids.

datA

 id swl1
 1            


        

Answer 1

IIUC, using data.table v1.9.5:

require(data.table)
setDT(datA)[datB, swl1 := swl2, on = "id"]

datA is updated by reference.